1. Field of the Invention
The present invention relates generally to a production line and more specifically to a robotized production line which enables the required degree in assembly precision to be achieved and minimize set up time and adjustment required to achieve the required precision.
2. Description of the Prior Art
A previously proposed assembly arrangement comprised the use of support arrangements each equipped with a number of gauge members on which panels could be supported and clamped in position. By moving either the support arrangement or bringing a structure such as a partially completed vehicle body, to the support, the panel could be held in the appropriate position with respect to the body and in a manner which faciliates spot welding of the panel to the same.
However, this arrangement has suffered from the drawbacks that the gauge members each required a hydraulic or pneumatically operated latch-like members which could be swung into position in a manner to clamp the panel (work piece) in position in the gauges during the welding or like operation. As the clamping members were required to be shaped so that when they were closed down on the gauge sections the resulting aperture corresponded to the cross-sectional shape of the panel or component to be supported by the same, the variety of panels and/or components which could be supported by any one support arrangement was severely limited.
Further, due to the rigidity distribution of the panels, when the latch-like members were swung to their released positions, the panels tended to, in some circumstances, undergo a "spring back" phenomenon or the like, and induce the situation wherein they tended to distort and or change position in an unintended manner.
To overcome this problem it was found necessary to isolate and manually adjust the positions of the problematical gauges in a manner wherein, when the clamping action was removed, the panels would not undergo undesirable changes in configuration and/or position. However, this adjustment has proven extremely time consuming and, in combination with the fact that when the line was modified and required the provision and set of new gauge members (including the above mentioned type of fine adjustment), was such as to badly impair the utility of the arrangement.
To overcome this problem an arrangement of the nature disclosed in JP-A-59-144595 and U.S. Pat. No. 4,691,905 issued on Sept. 8, 1987 in the name of Tamura et al, was proposed. This arrangement features the use of work piece locating devices which include gauge members which can be selectively shaped in accordance with the profile and shape of the work piece to be supported. Using these arrangements in combination with articulated robotic support arrangements which permit the gauges to be moved in three dimensions, a number of panels and components can be selectively moved into predetermined positional relationships with one and other wherein they can be spot welded together.
However, this type of arrangement has met with only partial success in that a long time is required to set up the system and once in operation requires constant surveilance in order to reset the various elements in the case of a drift in setting which permits the assembly accuracy to fall outside the permitted tolerances. Viz., in the case the robots are provided with a control program it is normal that an operator will "teach" each robot what to do during the initial set up stages. This teaching involves manually controlling the mechanism in a manner wherein the operator actually performs the assembly operation. Once the appropriate movements are recorded the robot is able to mimic the manually induced set of operations and thus reproduce the human ability. Accordingly, when a change in production is required an operator must re-teach the robots in accordance with the new or modified tasks which are now required. By way of example only, when the production of a sedan model changes to the corresponding stationwagon, while the forward end of the vehicle will remain essentially the same, the rear portion will have different panels and require that the robots be taught how to manipulate the same into place and secure the same by welding.